Swarms of earthquakes continue to rattle the Salton Sea area in Southern California, with more than a dozen sizable quakes since midnight, the U.S. Geological Survey reported Thursday.
Most of the tremors are below 3.0 magnitude, but a few earthquakes registering over 4.5 magnitude have been recorded, the USGS reports. The agency had recorded at least 240 quakes by Wednesday night.
“One of the largest swarms we have had in the Imperial Valley — and it is historically the most active swarms in SoCal,” seismologist Lucy Jones wrote on Twitter.
The quake swarms “are located in an area of diffuse seismic activity between the San Andreas fault in the north and the Imperial fault to the south.,” the USGS says. Previous swarms happened in 1991 and 2012.
The swarm most likely will continue for several days, possibly including quakes up to 5.4 magnitude, but there’s a slim chance of a major earthquake registering 7.0 magnitude or higher, the agency says.
The first swarm of 30 earthquakes rattled the area for one hour starting at 4 p.m. Wednesday, according to the USGS.
The first quake, a 3.0, hit near Westmorland. Another 27 quakes followed within the hour, all centered around Westmorland. More than half were magnitude 3.0 or greater, USGS data shows.
The following three scenarios describe possibilities of what could happen from 1 October to 8 October.
Only one of these scenarios will occur within the next week. These scenarios include the possibility of earthquakes on and off the Imperial and San Andreas Faults.
1. Scenario One (Most likely: 90%): Earthquakes continue, possibly including earthquakes up to magnitude 5.4.
The most likely scenario is that the rate of earthquakes in the swarm will decrease over the next 7 days. Some additional moderately sized earthquakes (M4.5 to 5.4) may occur, which could cause localized damage, particularly in weak structures. Smaller magnitude earthquakes (M3.0+) may be felt by people close to the epicenters.
2. Scenario Two (Less likely: 10%): A larger earthquake (magnitude 5.5 to 6.9) could occur within the next 7 days.
A less likely scenario is a somewhat larger earthquake could occur (up to a M6.9). Earthquakes of this size could cause damage around the area close to the earthquakes that have already occurred and would be followed by aftershocks that would increase the number of smaller earthquakes per day. This scenario occurred in a previous swarm in the area – in 1981, when a swarm in this region included a magnitude 5.8 earthquake.
3. Scenario Three (Least Likely: approximately 1 in 300): A much larger earthquake (magnitude 7 or higher) could occur within the next 7 days.
A much less likely scenario, compared with the previous two scenarios, is that the ongoing swarm could trigger an earthquake significantly larger than the M4.9 that occurred on the 30 September (i.e., M7.0 and above). While this is a very small probability, if such an earthquake were to occur, it would have serious impacts on communities nearby and would be followed by aftershocks that would increase the number of smaller earthquakes per day.
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